Some Final Comments On Both Technologies

Both technologies are extremely important to achieving high quality water characteristics, and both are complex - each posing a different set of challenges in scaling up to commercial size operations. You will find that most equipment suppliers have the expertise to tailor their equipment and processes to specific applications, but that in many situations, pilot scale testing will be required.

The overview of these technologies presented in this chapter should give you a flavor for the applications and general principles. For carbon adsorption, we can add one more helpful piece of information. Table 11 provides you with some representative organic chemicals that can be removed from water using activated carbon systems. Following this table is a short glossary of important terms for ion exchange and carbon adsorption.

Acidity: An expression of the concentration of hydrogen ions present in a solution.

Adsorbent: A synthetic resin possessing the ability to attract and to hold charged particles.

Adsorption: The attachment of charged particles to the chemically active group on the surface and in the pores of an ion exchanger.

Alkalinity: An expression of the total basic anions (hydroxy 1 groups) present in a solution. It also represents, particularly in water analysis, the bicarbonate, carbonate, and occasionally, the borate, silicate, and phosphate salts which will react with water to produce the hydroxy I groups.

Anion: A negatively charged particle or ion. Anion interchange: The displacement of one negatively charged particle by another on an anion-exchange material.

Attrition: The rubbing of one particle against another in a resin bed; frictional wear that will affect the site of resin particles.

Backwash: The countercurrent flow of water through a resin bed (that is, in at the bottom of the exchange unit, out at the top) to clean and regenerate the bed after exhaustion.

Base exchange: The property of the trading of cations shown by certain in- soluble naturally occurring materials (zeolites) and developed to a high degree of specificity and efficiency in synthetic resin adsorbents.

Batch operation: The utilization of ion-exchange resins to treat a solution in a container wherein the removal of ions is accomplished by agitation of the solution and subsequent decanting of the treated liquid.

Bed: A mass of ion-exchange resin particles contained in a column. Bed depth: The height of the resinous material in the column after the exchanger has been properly conditioned for effective operation. Bed expansion: The effect produced during backwashing when the resin particles become separated and rise in the column. The expansion of the. bed due to the increase in the space between resin particles may be controlled by regulating backwash flow.

Bicarbonate alkalinity: The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are produced, and the solution is alkaline.

Breakthrough: The first appearance in the solution flowing from an ion-ex- change unit of unabsorbed ions similar to those which are depleting the activity of the resin bed. Breakthrough is an indication that regeneration of the resin is necessary.

Capacity: The adsorption activity possessed in varying degrees by ion-ex- change materials. This quality may be expressed as kilograins per cubic foot, gram-milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, and so on, where the numerators of these ratios represent the weight of the ions adsorbed and the de- nominators represent the weight or volume of the adsorbent.

Carbonaceous exchangers: Ion-exchange materials of limited capacity pre- pared by the sulfonation of coal, lignite, peat, and so on.

Carboxylic: A term describing a specific acidic group (COOH) that contrib- utes cation-exchange ability to some resins.

Cation: A positively charged particle or ion. Channeling: Cleavage and furrowing of the bed due to faulty operational procedure, in which the solution being treated follows the path of least resistance, runs through these furrows, and fails to contact active groups in other parts of the bed.

Color-throw: Discoloration of the liquid passing through an ion-exchange material; the flushing from the resin interstices of traces of colored organic reaction intermediates.

Column operation: Conventional utilization of ion-exchange resins in columns through which pass, either upflow or downflow, the solution to be treated.

Cycle: A complete course of ion-exchange operation. For instance, a complete cycle of cation exchange would involve regeneration of the resin with acid, rinse to remove excess acid, exhaustion, backwash, and finally regeneration.

Deashing: The removal from solution of inorganic salts by means of adsorption by ion-exchange resins of both the cations and the anions that comprise the salts. See deionization.

Deionization: Deionization, a more general term than deashing, embraces the removal of all charged constituents or ionizable salts (both inorganic and organic) from solution.

ION EXCHANGE AND CARBON ADSORPTION 437 Demineralizing: See deashing.

Density: The weight of a given volume of exchange material, backwashed and in place in the column.

Dissociation: Ionization.

Downflow: Conventional direction of solutions to be processed in ion-ex- change column operation, that is, in at the top, out at the bottom of the column.

Dynamic system: An ion-exchange operation wherein a flow of the solution to be treated is involved.

Efficiency: The effectiveness of the operational performance of an ion ex- changer. Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, for example, pounds of acid per kilogram of salt removed.

Effluent: The solution which emerges from an ion-exchange column. Electrolyte: A chemical compound which dissociates or ionizes in water to produce a solution which will conduct an electric current; an acid, base, or salt.

Elution: The stripping of adsorbed ions from an ion-exchange material by the use of solutions containing other ions in concentrations higher than those of the ions to be stripped.

Equilibrium reactions: The interaction of ionizable compounds in which the products obtained tend to revert to the substance from which they were formed until a balance is reached in which both reactants and pacts are present in definite ratios.

Equivalent weight: The molecular weight of any element or radical expressed as grams, pounds, and so on divided by the valence.

Exchange velocity: The rate with which one ion is displaced from an ex- changer in favor of another.

Exhaustion: The state in which the adsorbent is no longer capable of useful ion exchange; the depletion of the exchanger's supply of available ions. The exhaustion point is determined arbitrarily in terms of: (1) a value in parts per million of ions in the effluent solution; and (2) the reduction in quality of the effluent water determined by a conductivity bridge which measures the resistance of the water to the flow of an electric current.

Fines: Extremely small particles of ion-exchange materials.

Flow rate: The volume of solution which passes through a given quantity of resin within a given time. Flow rate is usually expressed in terms of feet per minute per cubic foot of resin or as millimeters per minute per millimeter of resin.

Freeboard: The space provided above the resin bed in an ion-exchange column to allow for expansion of the bed during backwashing.

Grain: A unit of weight; 0.0648 grams; 0.000143 pounds.

Grains per gallon: An expression of concentration of material in solution. One grain per gallon is equivalent to 17.1 parts per million.

Gram: A unit of weight; 15.432 grains; 0.0022 pounds.

Gram-milliquivalents: The equivalent weight in grams, divided by 1,000.

Hardness: The scale-forming and lather-inhibiting qualities which water, high in calcium and magnesium ions, possesses.

Hardness as calcium carbonate: The expression ascribed to the value obtained when the hardness-forming salts are calculated in terms of equivalent quantities of calcium carbonate; a convenient method of reducing all salts to a common basic for comparison.

Head loss: The reduction in liquid pressure associated with the passage of a solution through a bed of exchange material; a measure of the resistance of a resin bed to the flow of the liquid passing through it.

Hydraulic classification: The rearrangement of resin particles in an ion-ex- change unit. As the backwash water flows up through the resin bed, the particles are placed in a mobile condition wherein the larger particles settle and the smaller particles rise to the top of the bed.

Hydrogen cycle: A complete course of cation-exchange operation in which the adsorbent is employed in the hydrogen or free acid form.

Hydroxyl: The term used to describe the anionic radical (OH-) which is responsible for the alkalinity of a solution.

Influent: The solution which enters an ion-exchange unit.

Ion: Any particle of less than colloidal size possessing either a positive or a negative electric charge.

Ionization: The dissociation of molecules into charged particles.

Ionization constant: An expression in absolute units of the extent of dissociation into ions of a chemical compound in solution.

Leakage: The phenomenon in which some of the influent ions are not ad- sorbed and appear in the effluent when a solution is passed through an underregenerated exchange resin bed.

Negative charge: The electrical potential which an atom acquires when it gains one or more electrons; a characteristic of an anion.

pH: An expression of the acidity of a solution; the negative logarithm of the hydrogen-ion concentration (pH 1 very acidic; pH 14, very basic; pH 7, neutral).

pOH; An expression of the alkalinity of a solution; the negative logarithm of the hydroxyl-ion concentration.

pK: An expression of the extent of dissociation of an electrolyte; the negative logarithm of the ionization constant of a compound.

Physical stability: The quality which an ion-exchange resin must possess to resist changes that might be caused by attrition, high temperatures, and other physical conditions.

Positive charge: The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.

Raw water: Untreated water from wells or from surface sources.

Regenerant: The solution used to restore the activity of an ion exchanger. Acids are employed to restore a cation exchanger to its hydrogen form; brine solutions may be used to convert the cation exchanger to the sodium form. The anion exchanger may be rejuvenated by treatment with an alkaline solution.

Regeneration: Restoration of the activity of an ion exchanger by replacing the ions adsorbed from the treated solution by ions that were adsorbed initially on the resin.

Rejuvenation: See regeneration.

Reverse deionization: The use of an anion-exchange unit and a cation-ex- change unit-in that order-to remove all ions from solution.

Rinse: The operation which follows regeneration; a flushing out of excess regenerant solution.

Siliceous gel zeolite: A synthetic, inorganic exchanger produced by the aqueous reaction of alkali with aluminum salts.

Static system: The batch-wise employment of ion-exchange resins, wherein (since ion exchange is an equilibrium reaction) a definite endpoint is reached in which a finite quantity of all the ions involved is present. Opposed to a dynamic, column-type operation.

Sulfonic: A specific acidic group (sojhj on which depends the exchange activity of certain cation adsorbents.

Swelling: The expansion of an ion-exchange W which occurs when the re- active groups on the resin are converted from one form to another.

Throughput volume: The amount of solution passed through an exchange W before exhaustion of the resin is reached.

Upflow: The operation of an ion-exchange unit in which solutions are passed in at the bottom and out at the top of the container.

Voids: The space between the resinous particles in an ion-exchange bed.

7. Ion Exchange for Introduction to Biochemical Engineering - General and company specific information - "Ion exchange can be defined as a reversible exchange of ions between a solid and a liquid in which there is no substantial change in the structure of the solid (Dowex Dow Chemical)". The solids are the ion exchange resin., etc. http://www.rpi.edu/dept/chem-eng/Biotech.

8. Ion Exchange Resins - Spectra/Gel Ion Exchange resins are ion exchange media for use in low-pressure liquid chromatography. They are based on a polystyrene/divinylbenzene support and are available for both anion and cation exchange applications. This site will give you a reasonable background on resin selection criteria and some economic factors for comparisons to other technologies, http://www.lplc.com/misc/ionex.htm..

9. Ion exchange for Metal Recovery - A discussion of the trade-offs Author Karrs, Stanley R. Buckley, Deborah Morey Document Type Proceedings article Source 7th AESF/EPA Conference on Pollution Control in the Metal Finishing Industry Subject Resource. Although specific to the metal industry, still some very good technical data that will assist you on resin selection for ion exchange applications. Also, some good schematics of process operations. http://es.epa.gOv/techpubs/0/7250.html.

10. Application of Ion Exchange to Materials Recovery - A compilation of links to internet recycling resources provided by Allan Barton of Murdoch University, author of Resources Recycling and Recovery. Visit this at the following URL... http://wwwscience.murdoch.edu.au/teachin.

11. Ion Exchange Resins - Very good site for you to visit! Contains cost comparisons between RO and ion exchange systems for several design cases. http://www. rohmhaas .com/ionexchange.

12. Comparison with Reverse Osmosis and Ion Exchange - Another great site to visit for comparison with reverse osmosis and ion exchange The BioDentmProcessReverse Osmosislon Exchange THE BioDentm PROCESS The BioDentm process has several important advantages over other nitrate treatment systems: http://www.nitrateremoval.com..

13. Ion Exchange Simulation - Uses the Java applet that simulates an ion exchange experiment. Select from topics for information on using the applet. Setting up the experiment Running the simulation. http://www.rit.edu/~pac8612/webionex/web.

14. JCE 1996 (73) 639 [Jul] Visible Ion Exchange Demonstration for Large or Small Lecture Halls - Visible Ion Exchange Demonstration for Large or Small Lecture Halls Jerry A. Driscoll Department of Chemistry, University of Utah, Salt Lake City, UT 84112 This demonstration is a colorful illustration of how an ion exchange column works. Some great visual graphics! http://jchemed.chem.wisc.edu.

adsorption and ion exchange group loughborough university department of chemical engineering The adsorption and ion exchange group is concerned with research into environmental pollution control, especially the removal of trace toxic metals and organochemicals. You will find abstracts of research and links to research articles. http://www-staff. lboro. ac .uk/ ~ cgbs2.

20. Home Water Treatment Using Activated Carbon - Discussion and guidelines from a 1997 article from the Michigan State University Extens ion. http: //www. msue. msu. edu/msue/imp/modwq/w.

25. Water Quality and Treatment Handbook, 5th Edition - State-of-the-art handbook of community water supplies The leading source of information on water quality, water treatment, and quality control for 60 years is now available in an up-to-the-minute new edition. Go to this site for detailed contents of this important publication. http://preview.mcgraw-hill.com/info/com.

29. Ground Water Pumping and Treatment - Last updated: 17-Jul-96 Ground Water Pumping and Treatment: extracts contaminated ground water and separates the contamination from the water, then destroys the contaminants. Techniques used to treat ground water including carbon adsorption are discussed, http://www.deq.state.la.us/remediation.

30. Home Water Treatment Using Activated Carbon - Michigan State University Extension MSU Extension Water Quality Bulletins - WQ239201 07/14/97 Home Water Treatment Using Activated Carbon Introduction Activated carbon (AC) filters. Useful site for residential applications in water purification, http://www.msue.msu.edu/imp/modwq/wq2392...

Recommend you check these hardcopy references out and add them to your library.

31. McPeak, John F. and Harold L. Aronovitch, Iron in Water and Processes for its Removal, Hungerford and Terry Inc., Clayton, N.J., 1983.

32. Guidelines for Canadian Drinking Water Quality, 4th ed., Minister of National Health and Welfare, Ottawa, 1989.

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